The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, HDDs have been desired to store more information in its limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
One method of recording which is capable of utilizing smaller components is referred to as microwave assisted magnetic recording (MAMR). For MAMR, a spin torque oscillator (STO) element or device is located next to or near the write element in order to produce a high-frequency oscillating magnetic field (in addition to a recording magnetic field emanated from a main pole of the write element) which reduces an effective coercivity of a recording medium used to store data.
In order to produce this high-frequency rotating or oscillating magnetic field with the STO, a very high current density (such as a current density on the order of 1×108 A/cm2) is passed through the STO device. Typically, a STO has a relatively small size, about the size of a read element, and a current much larger than that passed through the read element may be passed through the STO. Assuming typical dimensions and operating parameters for the STO, the temperatures reported in Table 1, below, are expected to be produced within the STO device upon passing current therethrough. The STO maximum temperatures depend on current density and thermal properties of all materials of the STO and in the path of the current. Table 1 shows two cases of STOs, STO1 and STO2, with write elements having different magnetic materials having different thermal properties, e.g., thermal conductivities of 25 and 80 W/in K, respectively.
TABLE IThermalSTOSTOSTOAppliedTotalCurrentSTOConductivityTmaxRavgPowerVoltageCurrentDensityVavgCase[W/(m · K)][° C.][Ohm][mW][V][A][A/cm2][V]STO12523975.40.510.20.00261.04 × 1080.196STO28012165.60.590.20.003 1.20 × 1080.197
The temperatures for STO1 and STO2, 239° C. and 121° C., respectively, are high enough to lead to reliability issues over the lifetime of a magnetic recording device employing the STOs, which may be considered to be anywhere from three to five years. It is undesirable to have the STO be a limiting factor in the reliability of a MAMR device.